1999 Chevy k1500 Truck 5.3 engine T Third brake light doesn't work?

[repster100]

My truck third brake light doesn't work. I checked all the fuses and replaced the bulbs and it still doesn't work. Does the third brake recieves its power from the brake light switch or does it have some sort of relay. I checked for power at the 4 wire pigtail connector. The cargo lights work but not the brake light.

 

[keierm]

check the switch at the base of your foot pedal if that dont work put a test light on it to see if its getting grounded out some where if the light dont come on , the tester there is a bad ground